6.1.4.2 Examples of ALWAYS, NEVER, and THEREIS clauses

;; Make sure I is always less than 11 (two ways).
;; The FOR construct terminates these loops.
(loop for i from 0 to 10
always (< i 11))
=> T
(loop for i from 0 to 10
never (> i 11))
=> T
;; If I exceeds 10 return I; otherwise, return NIL.
;; The THEREIS construct terminates this loop.
(loop for i from 0
thereis (when (> i 10) i) )
=> 11
;;; The FINALLY clause is not evaluated in these examples.
(loop for i from 0 to 10
always (< i 9)
finally (print "you won't see this"))
=> NIL
(loop never t
finally (print "you won't see this"))
=> NIL
(loop thereis "Here is my value"
finally (print "you won't see this"))
=> "Here is my value"
;; The FOR construct terminates this loop, so the FINALLY clause
;; is evaluated.
(loop for i from 1 to 10
thereis (> i 11)
finally (prin1 'got-here))
>> GOT-HERE
=> NIL
;; If this code could be used to find a counterexample to Fermat's
;; last theorem, it would still not return the value of the
;; counterexample because all of the THEREIS clauses in this example
;; only return T. But if Fermat is right, that won't matter
;; because this won't terminate.
(loop for z upfrom 2
thereis
(loop for n upfrom 3 below (log z 2)
thereis
(loop for x below z
thereis
(loop for y below z
thereis (= (+ (expt x n) (expt y n))
(expt z n))))))